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17 Jul 2000

Volume 77, Issue 3, pp. 313-459

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Characterizing the hard x-ray diffraction properties of a GaAs linear Bragg–Fresnel lens

Youli Li, Gerard C. L. Wong, Ryan Case, Cyrus R. Safinya, Ernie Caine, Evelyn Hu, and Partricia Fernandez

Appl. Phys. Lett. 77, 313 (2000); http://dx.doi.org/10.1063/1.126961 (3 pages) | Cited 4 times

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We investigated the diffractive focusing properties of (111) GaAs linear Bragg–Fresnel lenses (BFLs) developed for hard x-ray microscopy and microdiffraction of complex materials in confined geometries. We demonstrated that the use of GaAs yields significant processing advantages due to the reduced zone depth. Focal plane diffraction patterns of linear BFLs measured at the advanced photon source using 8–40 keV x rays were compared to a simple model based on Kirchhoff–Fresnel diffraction theory. Good agreement was obtained between experimental data and model calculations using only zones within an effective aperture defined by the transverse coherence of the source. © 2000 American Institute of Physics.
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07.85.Tt X-ray microscopes
42.79.Bh Lenses, prisms and mirrors
42.25.Fx Diffraction and scattering

Solar-blind AlGaN-based inverted heterostructure photodiodes

E. J. Tarsa, P. Kozodoy, J. Ibbetson, B. P. Keller, G. Parish, and U. Mishra

Appl. Phys. Lett. 77, 316 (2000); http://dx.doi.org/10.1063/1.126962 (3 pages) | Cited 39 times

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True solar-blind operation with a sharp responsivity cutoff at ∼300 nm has been demonstrated in AlGaN-based photodiodes using an “inverted heterostructure photodiode” design. This structure utilizes an AlxGa1−xN(x>0.3) intrinsic or lightly doped active layer surrounded by p- and/or n-type contact layers having a narrower band gap than the active layer. By utilizing narrow band gap (e.g., GaN) contact layers, the difficulties associated with achieving high doping efficiencies in wide band gap contact layers are circumvented. This basic structure is applicable to both front- and back-side illuminated detector geometries. Front-side illuminated solar-blind photodiodes were demonstrated with a peak responsivity of 0.08 A/W at 285 nm, while back-side illuminated detectors yielded a peak responsivity of 0.033 A/W at 275 nm (both are measured without antireflection coating). Both types of detectors offered sharp spectral responsivity cutoff of at least three orders of magnitude by 325 nm. © 2000 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide

Valentina S. U. Fazio, Sven T. Lagerwall, Philippe Busson, Anders Hult, and Hubert Motschmann

Appl. Phys. Lett. 77, 319 (2000); http://dx.doi.org/10.1063/1.126963 (3 pages) | Cited 3 times

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True phase-matched second-harmonic generation in a waveguide of crosslinkable ferroelectric liquid crystals is demonstrated. These materials allow the formation of macroscopically polar structures whose order can be frozen by photopolymerization. Homeotropic alignment was chosen which offers decisive advantages compared to other geometries. All parameters contributing to the conversion efficiency are maximized by deliberately controlling the supramolecular arrangement. The system has the potential to achieve practical level of performances as a frequency doubler for low power laser-diodes. © 2000 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.79.Kr Display devices, liquid-crystal devices
42.79.Nv Optical frequency converters

Electron drift mobility in pyrazolo[3,4-b]quinoline doped polystyrene layers

A. R. Tameev, Z. He, G. H. W. Milburn, A. A. Kozlov, A. V. Vannikov, A. Danel, and P. Tomasik

Appl. Phys. Lett. 77, 322 (2000); http://dx.doi.org/10.1063/1.126964 (3 pages) | Cited 10 times

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Pyrazolo[3,4-b]quinoline derivatives are found to have electron transport properties. A field dependent electron drift mobility, in the range of 10−6–3×10−5 cm2/(V s) at an electric field of (1–7)×105 V/cm, has been found from the pyrazolo[3,4-b]quinoline doped polystyrene specimen, which was measured using a conventional time-of-flight method. The results are fit well into a correlated disorder model for a dipole medium when energetic features of the transport molecules are also taken into account. © 2000 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
71.20.Rv Polymers and organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance

High-frequency properties of 1.55 μm laterally complex coupled distributed feedback lasers fabricated by focused-ion-beam lithography

S. Rennon, L. Bach, J. P. Reithmaier, A. Forchel, J. L. Gentner, and L. Goldstein

Appl. Phys. Lett. 77, 325 (2000); http://dx.doi.org/10.1063/1.126965 (3 pages) | Cited 9 times

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Laterally complex coupled distributed feedback lasers have been fabricated by focused-ion-beam lithography on completely grown InGaAsP/InP laser structures emitting at 1.55 μm. The grating definition is based on implantation-enhanced quantum-well intermixing and wet chemical etching and allows the fabrication of complex coupled antiphase gratings without any further overgrowth step. Side-mode suppression ratios of 45 dB and bandwidths for direct modulation beyond 13 GHz were obtained for 300-μm-long devices. The lasers exhibit frequency-modulation response values lower than 200 MHz/mA and feature a low sensitivity to back-reflected light. Preliminary lifetime measurements over 7000 h continuous-wave operation at room temperature show no significant indication for long-time degradation. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings

Photoluminescence studies and read/write process of a strong two-photon absorbing chromophore

R. Sivaraman, S. J. Clarson, B. K. Lee, A. J. Steckl, and B. A. Reinhardt

Appl. Phys. Lett. 77, 328 (2000); http://dx.doi.org/10.1063/1.126966 (3 pages) | Cited 11 times

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The optical properties of a fluorene-based chromophore exhibiting a high two-photon absorption cross section have been investigated both in the pure state and as a guest–host system in poly(N-vinylcarbazole). Upon irradiation with a helium cadmium (He–Cd) laser at 325 nm, the guest–host sample exhibits a blueshift with a maximum emission at 459 nm. Information written onto the samples in the blue can also be read using an Ar+ laser. The chromophore undergoes a chemical change upon irradiation in air, and has been found to no longer exhibit upconversion after this transformation. Infrared analysis of the sample (the chromophore) before and after irradiation was carried out, and the spectra suggest the formation of a new conjugated species. Other applications we have developed using this phenomenon include the successful writing of optical device structures in polymer films where the AF-50 is a guest material. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
42.79.Vb Optical storage systems, optical disks

High-efficiency organic dye-doped polymer optical fiber lasers

Ken Kuriki, Takeyuki Kobayashi, Nana Imai, Toshihiko Tamura, Susumu Nishihara, Yukihisa Nishizawa, Akihiro Tagaya, Yasuhiro Koike, and Yoshi Okamoto

Appl. Phys. Lett. 77, 331 (2000); http://dx.doi.org/10.1063/1.126967 (3 pages) | Cited 15 times

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A graded-index polymer optical fiber containing rhodamine 6G in poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) has been fabricated. Lasing behavior of the fiber was observed by pumping with a frequency-doubled Q-switched Nd: yttrium–aluminum–garnet laser. A slope efficiency of 43% and a lifetime of 110 000 shots at a repetition rate of 10 Hz have been observed. With a 1.5 mJ pump energy, an output energy of 640 μJ was produced. © 2000 American Institute of Physics.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.55.Mv Dye lasers
42.81.Ht Gradient-index (GRIN) fiber devices

Intersubband absorption in GaN/AlGaN multiple quantum wells in the wavelength range of λ ∼ 1.75–4.2 μm

Claire Gmachl, Hock M. Ng, and Alfred Y. Cho

Appl. Phys. Lett. 77, 334 (2000); http://dx.doi.org/10.1063/1.126968 (3 pages) | Cited 5 times

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Intersubband optical absorption in narrow, 15–30 Å wide, GaN/AlGaN quantum wells has been measured. The samples were grown by molecular-beam epitaxy on sapphire substrate and the barrier AlN mole fraction was varied from 0.45 to 0.8. Peak absorption wavelengths ranged from 4.2 μm for 30 Å wide wells to 1.77 μm for a 15 Å wide well. Modeling shows that a large contribution to the considerable spectral width of the absorption of ∼150 meV likely results from monolayer fluctuations. In addition to the composition dependent band offset, the intrinsic electric fields in the wells and barriers are the determining factors for the shortest possible wavelength. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Low-noise and high-gain image amplification by contradirectional two-wave mixing

Xiaodong Mu, Xinguang Xu, Zongshu Shao, Minhua Jiang, and Haosu Luo

Appl. Phys. Lett. 77, 337 (2000); http://dx.doi.org/10.1063/1.126969 (3 pages)

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Contradirectional two-wave mixing (CTWM) is demonstrated to be a perfect configuration for low-noise and high-gain image amplification. Compared with the image amplified by the forward two-wave mixing configuration, the signal-to-noise ratio is increased from 6 to 2×104 in the experiments in Rh-doped BaTiO3 crystal. The gain of the signal beam is also enhanced effectively. We have contrasted the differences between the two experimental configurations and gave a credible explanation for the low noise and high gain that exists in the CTWM configuration. © 2000 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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Electric field-induced layer deformations in the subphases of an antiferroelectric liquid crystal device

L. S. Matkin, H. F. Gleeson, L. J. Baylis, S. J. Watson, N. Bowring, A. Seed, M. Hird, and J. W. Goodby

Appl. Phys. Lett. 77, 340 (2000); http://dx.doi.org/10.1063/1.126970 (3 pages) | Cited 20 times

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The layer structure in the antiferroelectric, ferrielectric, and ferroelectric phases of a liquid crystal device is reported, together with its electric field-induced deformation. The field-free chevron angle is comparable to the steric tilt angle, but differs significantly from the optical tilt angle. A sharp field threshold is observed for the chevron to bookshelf transition in the antiferroelectric phase at 1.3 V/μm, while layer deformations occur at much lower fields (0.3 V/μm) in the other subphases. Models are proposed for the layer deformations. © 2000 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
42.79.Kr Display devices, liquid-crystal devices
64.70.M- Transitions in liquid crystals

Molecular-dynamics study of the mechanism and kinetics of void growth in ductile metallic thin films

M. Rauf Gungor, Dimitrios Maroudas, and Shujia Zhou

Appl. Phys. Lett. 77, 343 (2000); http://dx.doi.org/10.1063/1.126971 (3 pages) | Cited 12 times

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A molecular-dynamics study is presented of the mechanism and kinetics of void growth and morphological evolution in ductile metallic thin films subject to biaxial tensile strains. The void becomes faceted, grows, and relieves strain by emission from its surface of pairs of screw dislocations with opposite Burgers vectors. Repeated dislocation generation and propagation leads to formation of a step pattern on the film’s surfaces. A simple phenomenological kinetic model of void growth is derived. Such kinetic equations can be used to formulate constitutive theories of plastic deformation for continuum-scale modeling of void evolution. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Qq Microscopic defects (voids, inclusions, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation
68.60.Bs Mechanical and acoustical properties
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Yx Interaction between different crystal defects; gettering effect
68.35.B- Structure of clean surfaces (and surface reconstruction)

Phonon deformation potentials of α-GaN and -AlN: An ab initio calculation

J.-M. Wagner and F. Bechstedt

Appl. Phys. Lett. 77, 346 (2000); http://dx.doi.org/10.1063/1.127009 (3 pages) | Cited 70 times

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First-principles density functional theory calculations of the deformation potentials are presented for zone-center phonons in GaN and AlN in the wurtzite structure. Three cases of deformations are considered: biaxial and uniaxial strain along the c axis as well as hydrostatic compression. For the resulting atomic structures the phonon frequencies are determined. The combination of calculations for these deformations allows the derivation of elastic constants and phonon deformation potentials. Good agreement is observed with measured values for GaN. No published values for AlN are available. © 2000 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
62.20.D- Elasticity
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Structural evolution of ZnO/sapphire(001) heteroepitaxy studied by real time synchrotron x-ray scattering

Sang Il Park, Tae Sik Cho, Seok Joo Doh, Jong Lam Lee, and Jung Ho Je

Appl. Phys. Lett. 77, 349 (2000); http://dx.doi.org/10.1063/1.126972 (3 pages) | Cited 16 times

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The structural evolution during heteroepitaxial growth of ZnO/sapphire(001) by radio-frequency magnetron sputtering has been studied using real-time synchrotron x-ray scattering. The two-dimensional (2D) ZnO(002) layers grown in the initial stage are highly strained and well aligned to the substrate having a mosaic distribution of 0.01° full width at half maximum (FWHM), in sharp contrast to the reported transition 2D layers grown by molecular-beam epitaxy. With increasing film thickness, the lattice strain is relieved and the poorly aligned (1.25° FWHM) three-dimensional (3D) islands are nucleated on the 2D layers. We attribute the 2D–3D transition to the release of the strain energy stored in the film due to the film/substrate lattice mismatch. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
61.05.cf X-ray scattering (including small-angle scattering)
81.05.Dz II-VI semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Use of scanned laser annealing to control the bamboo grain length of Cu interconnects

C. S. Hau-Riege and C. V. Thompson

Appl. Phys. Lett. 77, 352 (2000); http://dx.doi.org/10.1063/1.126973 (3 pages) | Cited 3 times

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Microstructural evolution induced by scanned laser annealing (SLA) of Cu interconnects was found to produce unique large-grained “bamboo” grain structures, with bamboo grain lengths up to ten times the linewidth. These bamboo grain lengths are shown to depend on the scan rate and laser power. By comparing results from experiments on different structures with grain growth simulations, the bamboo grain length induced by SLA is shown to be a strong function of the thermal profile, where steeper thermal profiles yield longer bamboo grains. © 2000 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
61.72.Cc Kinetics of defect formation and annealing
68.55.-a Thin film structure and morphology

Two-photon absorption in GaN, GaInN, and GaAlN alloys

Srinivasan Krishnamurthy, Karen Nashold, and A. Sher

Appl. Phys. Lett. 77, 355 (2000); http://dx.doi.org/10.1063/1.126974 (3 pages) | Cited 10 times

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We have carried out full band-structure-based studies of two-photon absorption coefficients in the GaN compound, and GaInN and GaAlN alloys. An accurate Hamiltonian and resulting wave functions and band structures are used in the calculations. The coefficients in GaN calculated without any adjustable parameters agree very well with recent experiments. We further show that the two-photon absorption coefficients can be increased or decreased by adding In or Al to the GaN compound. The spectral variation of the absorption coefficient can be explained in terms of the alloy-induced changes in the band gap and joint density of states. © 2000 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Interdiffusion in NiFe/Cu/NiFe trilayers: Possible failure mechanism for magnetoelectronic devices

W. Brückner, S. Baunack, M. Hecker, J.-I. Mönch, L. van Loyen, and C. M. Schneider

Appl. Phys. Lett. 77, 358 (2000); http://dx.doi.org/10.1063/1.126975 (3 pages) | Cited 10 times

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The evolution of electrical resistance, stress, and microstructure during annealing has been studied on 100 nm NiFe(20 wt %)/200 nm Cu/100 nm NiFe trilayers. Irreversible resistance changes and the concentration-depth profiles show that, at and above 200 °C, diffusion of Ni into Cu as well as of Cu into NiFe occurs. The interdiffusion is held for an important failure mechanism of Cu/NiFe-based magnetoelectronic system at elevated temperatures. © 2000 American Institute of Physics.  
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68.35.Fx Diffusion; interface formation
75.47.De Giant magnetoresistance
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.At Metal and metallic alloys
66.30.Ny Chemical interdiffusion; diffusion barriers
75.50.Bb Fe and its alloys
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Measurement of nanohardness and nanoelasticity of thin gold films with scanning force microscope

B. Kracke and B. Damaschke

Appl. Phys. Lett. 77, 361 (2000); http://dx.doi.org/10.1063/1.126976 (3 pages) | Cited 23 times

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With a scanning force microscope operating in ultrahigh vacuum, we measured local mechanical properties of single crystalline gold islands. The elastic moduli of the gold islands and the substrates sapphire, mica, and quartz were evaluated from force-distance curves. The value of Young’s elastic modulus in [111] direction of the gold grains is (50±16) GPa and was found to be significantly smaller than the bulk modulus of gold. With an indentation technique, the nanohardness of gold islands was investigated. The nanohardness is smaller than the bulk value and depends on the indentation area. This can be interpreted as nanohardening by dislocation interaction in very pure single crystals. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness

Synthesis and properties of epitaxial thin films of c-axis oriented metastable four-layered hexagonal BaRuO3

M. K. Lee, C. B. Eom, W. Tian, X. Q. Pan, M. C. Smoak, F. Tsui, and J. J. Krajewski

Appl. Phys. Lett. 77, 364 (2000); http://dx.doi.org/10.1063/1.126977 (3 pages) | Cited 12 times

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We have grown epitaxial thin films of c-axis oriented metastable four-layered hexagonal BaRuO3 on a (111) SrTiO3 substrate by 90° off-axis sputtering techniques. X-ray diffraction and transmission electron microscopy reveal that the films are single domains of c-axis four-layered hexagonal structures with an in-plane epitaxial arrangement of BaRuO3 [2mathmath0]∥SrTiO3[110]. Surfaces with smooth terraces having a step height of a half unit cell (∼4.7 Å) have been observed by scanning tunneling microscopy. The in-plane electrical resistivity of the films is metallic, with a room temperature value of 810 μΩ cm and slightly curved temperature dependence. Their magnetic susceptibility is Pauli paramagnetic. The metastable layered metallic oxide can be used for understanding new solid-state phenomena and device applications. © 2000 American Institute of Physics.
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81.15.Cd Deposition by sputtering
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.At Metal and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.20.Ck Nonmetals
68.35.B- Structure of clean surfaces (and surface reconstruction)

Independent determination of Ge content in thin Si1−xGex quantum wells by spectroscopic ellipsometry

M. Broschwitz, K. Dettmer, and J. Schoenes

Appl. Phys. Lett. 77, 367 (2000); http://dx.doi.org/10.1063/1.126978 (3 pages) | Cited 2 times

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The pseudodielectric functions of Si1−xGex multi-quantum-well samples have been measured by spectroscopic ellipsometry in the photon energy range from 1.1 to 4.5 eV at room temperature. A sharp structure near 3.2 eV, obtained in all our spectra, is identified as an interband transition of the Si1−xGex well, whose exact energy depends on x. By fitting line shapes to the second derivative of the spectra it is possible to determine the Ge content x of the thin Si1−xGex wells. The detailed analysis of the transition energies in comparison with x-ray diffraction data then allows the exact determination of the thicknesses of barriers and wells. The theoretically calculated shift of the transition energies caused by the strain of the Si1−xGex wells was taken into account in our analysis. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Hd Other semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Strain and composition of capped Ge/Si self-assembled quantum dots grown by chemical vapor deposition

G. Patriarche, I. Sagnes, P. Boucaud, V. Le Thanh, D. Bouchier, C. Hernandez, Y. Campidelli, and D. Bensahel

Appl. Phys. Lett. 77, 370 (2000); http://dx.doi.org/10.1063/1.126979 (3 pages) | Cited 21 times

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We have investigated the composition and the strain profile of Ge/Si self-assembled quantum dots. The quantum dots, grown by low-or high-pressure chemical vapor deposition, were covered by a silicon cap layer. The composition and the strain were measured by the selected area transmission electron diffraction of a single quantum dot. The self-assembled quantum dots exhibit a quadratic deformation. No lateral relaxation of the lattice is observed from the main part of the quantum dot. An average composition of Ge around 50% is deduced. The average composition is found dependent on the size of the islands. This composition is correlated to the photoluminescence energy. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
81.05.Cy Elemental semiconductors

Guided self-assembly of Au nanocluster arrays electronically coupled to semiconductor device layers

Jia Liu, Takhee Lee, D. B. Janes, B. L. Walsh, M. R. Melloch, J. M. Woodall, R. Reifenberger, and R. P. Andres

Appl. Phys. Lett. 77, 373 (2000); http://dx.doi.org/10.1063/1.126980 (3 pages) | Cited 9 times

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We report the controlled deposition of close-packed monolayer arrays of ∼ 5-nm-diam Au clusters within patterned regions on GaAs device layers, thus demonstrating guided self-assembly on a substrate which can provide interesting semiconductor device characteristics. Uniform nanometer scale ordering of the clusters is achieved by a chemical self-assembly process, while micron scale patterning is provided by a soft lithographic technique. Scanning tunneling microscope imaging and current–voltage spectroscopy indicate the Au nanoclusters are strongly coupled electronically into the underlying semiconductor substrate while exhibiting only weak electronic coupling in the lateral plane. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
61.46.-w Structure of nanoscale materials
73.40.Ns Metal-nonmetal contacts
73.22.-f Electronic structure of nanoscale materials and related systems
68.18.-g Langmuir-Blodgett films on liquids
81.05.Bx Metals, semimetals, and alloys

Temperature-dependent retardation effect of dopants on oxygen diffusion in heavily doped Czochralski silicon

Hiroshi Takeno, Ken Sunakawa, and Masashi Suezawa

Appl. Phys. Lett. 77, 376 (2000); http://dx.doi.org/10.1063/1.126981 (3 pages) | Cited 10 times

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The influence of boron (B), arsenic (As), and antimony (Sb) on oxygen diffusivity at 500–800 °C was investigated in heavily doped Czochralski silicon wafers with resistivities below 0.02 Ω cm. The oxygen diffusivity was determined from the outdiffusion profile measured by secondary ion mass spectrometry after prolonged heat treatments. It was found that the heavily doped As and Sb reduce the oxygen diffusivity more at lower temperature. The increases in the activation energy for diffusion were found to be about 0.64–0.68 and 1.40 eV for As and Sb doping, respectively. Heavy B doping, however, exhibited anomalous temperature dependence showing a reduction rate peak around 600–700 °C, supposedly due to enhanced formation of immobile oxygen aggregates. © 2000 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.S- Impurities in crystals
64.75.-g Phase equilibria
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Cc Kinetics of defect formation and annealing

Dynamical analysis of the buildup process near resonance

Jorge Villavicencio and Roberto Romo

Appl. Phys. Lett. 77, 379 (2000); http://dx.doi.org/10.1063/1.126982 (3 pages) | Cited 10 times

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The time evolution of the buildup process inside a double-barrier system for off-resonance incidence energies is studied by considering the analytic solution of the time-dependent Schrödinger equation with cutoff plane wave initial conditions. We show that the buildup process exhibits invariances under arbitrary changes on the system parameters, which can be successfully described by a simple and easy-to-use one-level formula. We find that the buildup of the off-resonant probability density is characterized by an oscillatory pattern modulated by the resonant case which governs the duration of the transient regime. This is evidence that off-resonant and resonant tunneling are two correlated processes, whose transient regime is characterized by the same transient time constant of two lifetimes. © 2000 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling
03.65.Ge Solutions of wave equations: bound states

Low resistance ohmic contacts to n-GaN and n-AlGaN using NiAl

D. B. Ingerly, Y. Chen, R. S. William, T. Takeuchi, and Y. A. Chang

Appl. Phys. Lett. 77, 382 (2000); http://dx.doi.org/10.1063/1.126983 (3 pages) | Cited 13 times

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The intermetallic compound NiAl (50:50 at. %) has been shown to be a low-resistance ohmic contact to n-GaN and n-AlGaN. NiAl contacts on n-GaN (n = 2.5×1017 cm−3) had a specific contact resistance of 9.4×10−6 Ω cm2 upon annealing at 850 °C for 5 min. NiAl contacts annealed at 900 °C for 5 min in n-Al0.12Ga0.88N (n = 2.4×1018 cm−3) and n-Al0.18Ga0.82N (n = 2.7×1018 cm−3) had specific contact resistances of 2.1×10−5 Ω cm2 and 4.7×10−5 Ω cm2, respectively. Additionally, these contacts were subjected to long-term annealing at 600 °C for 100 h. On n-GaN, the contact specific contact resistance degraded from 9.4×10−6 Ω cm2 to 5.3×10−5 Ω cm2 after the long-term anneal. Contacts to n-Al0.18Ga0.82N showed only slight degradation with a change in contact resistance, from 4.7×10−5 Ω cm2 to 9.2×10−5 Ω cm2. These results demonstrate the NiAl has great promise as a stable, low-resistance contact, particularly to n-AlGaN used in high-temperature applications. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing

Optical properties of InAs quantum dots formed on GaAs pyramids

Haiyan An and Junichi Motohisa

Appl. Phys. Lett. 77, 385 (2000); http://dx.doi.org/10.1063/1.126984 (3 pages) | Cited 5 times

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Optical properties of InAs quantum dots on GaAs pyramidal structures formed by selective area metal organic vapor phase epitaxy have been studied with low-temperature excitation powerdependent microphotoluminescence (μ-PL) and microphotoluminescence excitation (μ-PLE) spectroscopy. The power-dependent μ-PL spectra show well-defined ground and excited states whose interlevel energy spacings are estimated to be about 21 meV. These experimental results demonstrate the discrete nature of zero-dimensional density of states in position and number controlled InAs quantum dots (QDs) selectively grown on GaAs pyramids. We have also observed relative strong PLE peaks which are ascribed to the multiple longitudinal optical phonon resonance. Excited states and carrier relaxation of InAs QDs formed on GaAs pyramids are discussed. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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